oracle/graal · error · ParserException.ClassFormatError

Array with more than 255 dimensions {}

Error message

Array with more than 255 dimensions {}

What it means

For array descriptors, skipValidTypeDescriptor counts leading '[' characters; the JVM spec limits arrays to 255 dimensions. More than 255 consecutive '[' throws ParserException.ClassFormatError 'Array with more than 255 dimensions <rest-of-descriptor>' before recursing into the element type.

Source

Thrown at espresso-shared/src/com.oracle.truffle.espresso.classfile/src/com/oracle/truffle/espresso/classfile/descriptors/TypeSymbols.java:239

            return beginIndex + 1;
        }
        switch (ch) {
            case 'L': {
                final int endIndex = skipClassName(descriptor, beginIndex + 1, slashes ? '/' : '.');
                if (endIndex > beginIndex + 1 && endIndex < descriptor.length() && descriptor.byteAt(endIndex) == ';') {
                    return endIndex + 1;
                }
                throw new ParserException.ClassFormatError("Invalid Java name " + descriptor.subSequence(beginIndex));
            }
            case '[': {
                // compute the number of dimensions
                int index = beginIndex;
                while (index < descriptor.length() && descriptor.byteAt(index) == '[') {
                    index++;
                }
                final int dimensions = index - beginIndex;
                if (dimensions > 255) {
                    throw new ParserException.ClassFormatError("Array with more than 255 dimensions " + descriptor.subSequence(beginIndex));
                }
                return skipValidTypeDescriptor(descriptor, index, slashes);
            }
        }
        throw new ParserException.ClassFormatError("Invalid type descriptor " + descriptor.subSequence(beginIndex));
    }

    /**
     * Gets the type descriptor for the specified component type descriptor with the specified
     * number of dimensions. For example if the number of dimensions is 1, then this method will
     * return a descriptor for an array of the component type; if the number of dimensions is 2, it
     * will return a descriptor for an array of an array of the component type, etc.
     *
     * @param type the type descriptor for the component type of the array
     * @param dimensions the number of array dimensions
     * @return the canonical type descriptor for the specified component type and dimensions
     */
    public Symbol<Type> arrayOf(Symbol<Type> type, int dimensions) {

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Cap array nesting in your generator at 255 dimensions and assert on it
2. Fix the recursive loop that keeps adding dimensions (usually a missing termination condition)
3. Validate incoming descriptors with a dimension count check before parsing

Example fix

// before
while (someCondition) { desc = "[" + desc; } // unbounded

// after
int dims = 0;
while (someCondition && dims < 255) { desc = "[" + desc; dims++; }

int dims = 0; while (dims < desc.length() && desc.charAt(dims) == '[') dims++;
if (dims > 255) throw new IllegalArgumentException("Array dimensions " + dims + " exceed 255: " + desc);

static boolean dimensionCountOk(String d) { int n = 0; while (n < d.length() && d.charAt(n) == '[') n++; return n <= 255; }

catch (ParserException.ClassFormatError e) { report dimension count and cap recursion in the generator }

When it happens

Trigger: Descriptors with 256+ leading '[' — usually produced by a loop that prepends '[' per array nesting level (e.g. recursive type mapping) or by a generator bug adding dimensions each iteration.

Common situations: Recursive generic array conversion where each recursion adds a dimension; fuzzed/malformed class files; copy loops that never terminate but append '[' each pass.

Related errors

• unknown primitive or void type character:
• invalid descriptor: {}
• invalid type descriptor: {}
• Invalid Java name {}
• Invalid type descriptor {}

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/1c7d6cc1bf480b31. Report an issue: GitHub.